Posted by
Michael J. Linden on
Dec 22, 2004; 3:02am
URL: http://elecraft.85.s1.nabble.com/K2-VFO-Drift-and-Temperature-Compensated-PLL-Reference-Upgrade-tp372782.html
I'm trying to understand a bit more about temperature-related VFO
drift in the K2. My K2 sits in the basement where it is currently seeing
stable ambient temperatures around 67F. When using 10 MHz WWV as a
reference, I see approximately 40 Hz of drift (10,000.03 to 9,999.99)
over a 30 to 45 minute period from a cold start. I am not transmitting
during this period, I assume this is just due to a slight heating (can't
be much of a temperature change) of various resistors, capacitors,
inductors, and varactors. This is clearly in-specification as it is much
less than the 100 Hz that is specified in the manual. ;^)
My K2 is serial number 4137, so it has had the Temperature-Compensated
PLL Reference Upgrade from the start. The Temperature-Compensated PLL
Reference Upgrade documentation says that you can check the VFO drift by
transmitting for a while to raise the temperature of the radio 15 or 30
degrees F _AFTER_ you have allowed a warm-up period of 30 or more
minutes. This appears to infer that there is a difference in the nature
between warm-up drift and post warm-up drift. If so, can someone explain
what that difference is?
I haven't performed the formal post warm-up drift testing, but I plan
to give it a try to see how stable the VFO is after warm-up. This raises
another question... Will making any changes to resistor RA on the PLL
thermistor board have any affect on the 40 Hz of warm-up drift (as
opposed to the post warm-up drift), or is this something that can't
really be addressed by the Temperature-Compensated PLL Reference
circuit?
Thanks, Michael N9BDF
PS It was nice to see that resistor RA was placed at the top of the PLL
thermistor board -- makes it much easier to fine tune the temperature
compensation! :^)
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